This invention relates to an image forming apparatus which uses an electrophotographic system, such as a copier, a printer, and a facsimile, and which has functions thereof. In particular, this invention relates to an image forming apparatus in which the toner image that is carried on the surface of the image carrier of a photoreceptor or the like is caused to contact and transfer to a transfer material by a transfer section, and the plurality of color toner images formed on an intermediate transfer member are superposed and transferred to the transfer material.
Examples of known image forming apparatuses in which a toner image that is carried on the surface of a toner image carrier and the like is caused to contact and transfer to the transfer material using a transfer section are described in the following documents.
Unexamined Japanese Patent Application Publication No. 05-61365 is an image forming apparatus that has a means for bringing the recording sheet in close contact with the belt-shaped photoreceptor at a position immediately before the transfer position.
Unexamined Japanese Patent Application Publication No. 08-146860 is an image forming apparatus which comprises contact varying means for changing contact pressure applied to the image carrier, which is the transfer roller, in accordance with the components of the toner inside the process cartridge and the size of the transfer material.
Unexamined Japanese Patent Application Publication No. 2002-156839 is an image forming apparatus which comprises a detection section for determining a member to be transferred by the transfer section that has a back-up roller and an intermediate transfer member; and a controller for controlling the pressing pressure of the member to be transferred using the backup roller in accordance with type of member to be transferred that was determined by the detection section.
Unexamined Japanese Patent Application Publication No. 2005-258288 is an image forming apparatus which obtains the sheet type data for transfer material from the sheet type detection section and based on this data, the transfer time for the transfer material and the contact conditions for the image carrier such as the length of the transfer nip width and timing of transfer material arrival are varied.
Unexamined Japanese Patent Application Publication No. 05-127458 is an image forming apparatus in which the contact positions of the image carrier and the transfer member comprise a first position at the time of the first surface printing of the transfer material; and a second position at the time of the second surface printing which is different from the first position, and by changing the first and second position when printing of the both the first surface and the second surface is performed, the transfer material ejection angle which is formed between the image carrier and the contact and transfer member is changed.
In the prior art technology disclosed in Unexamined Japanese Patent Application Publication Nos. 05-61365, 08-146860, and 2002-156839, and 2005-258288, the contact position where the transfer member contacts the image carrier is fixed, and the contact pressure in the transfer section and the transfer nip width are variable and are set to prescribed values with reference to sheet feeding performance, separation performance, transfer performance and the like of the transfer material.
However, depending on whether the transfer material is a thick sheet or thin sheet, the transfer material that is ejected from the transfer section may have reduced image quality due to separation failure, sliding contact on the eject guide plate in the vicinity of the rear end of the transfer material, flipping of the rear end of the transfer material and the like.
In the prior art technology disclosed in Unexamined Japanese Patent Application Publication No. 05-127458, the contact positions of the image carrier (photoreceptor drum) and the transfer member (transfer roller) comprise a first position at the time of first surface printing of the transfer material and a second position at the time of second surface printing which different from the first position, and this solves the problems occurring when transfer materials are conveyed at the time of printing of both surfaces. In addition, a means for varying entry of the transfer material into the transfer section and ejection of the transfer material from the transfer section may be considered.
One aspect of the present invention is an image forming apparatus including: an image forming section for forming a toner image on a photoreceptor; a primary transfer section for transferring the toner image formed in the image forming section to an intermediate transfer belt; a back-up roller that is arranged at the inner periphery side of the intermediate transfer belt; a secondary transfer roller that is in pressure contact with the back-up roller via the intermediate transfer belt and transfers the toner image from the intermediate transfer belt onto the transfer material while conveying the transfer material; a thickness information obtaining section which obtains information relating to the thickness of the transfer material; a moving mechanism which moves a position where the secondary transfer roller is in contact with the back-up roller via the intermediate transfer belt; and a controller which controls the moving mechanism based on the information relating to the thickness of the transfer material obtained by the thickness information obtaining section.
Another aspect of the present information is an image forming apparatus including: an image forming section for forming a toner image on a photoreceptor belt; a back-up roller that is arranged at the inner periphery side of the photoreceptor belt; a transfer roller that is in pressure contact with the back-up roller via the photoreceptor belt and transfers the toner image from the photoreceptor belt to the transfer material while conveying the transfer material; a thickness information obtaining section which obtains information relating to the thickness of the transfer material; a moving mechanism which moves a position where the transfer roller is in contact with the back-up roller via the photoreceptor belt; and a controller which controls the moving mechanism based on the information relating to the thickness of the transfer material obtained by the thickness information obtaining section.
Still another aspect of the present invention is an image forming apparatus including: an image forming section for forming a toner image on a photoreceptor; a primary transfer section for transferring the toner image formed in the image forming section to an intermediate transfer drum; a secondary transfer roller that is in pressure contact with the intermediate transfer drum and transfers the toner image from the intermediate transfer drum to the transfer material while conveying the transfer material; a thickness information obtaining section which obtains information relating to the thickness of the transfer material; a moving mechanism which moves a position where the secondary transfer roller is in contact with the intermediate transfer drum; and a controller which controls the moving mechanism based on the information relating to the thickness of the transfer material obtained by the thickness information obtaining section.